There exist a plurality of multiple access technologies in wireless communication system, such as code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), and so on. With the development of wireless communication technology, new multiple access technologies including space division multiple access (SDMA) and orthogonal frequency division multiple access (OFDMA), are emerging continuously.
Each multiple access technology has its own features, wherein FDMA divides the total system bandwidth into several non-overlapped sub-bands, each of which is allocated to a user; TDMA divides each channel into several time slots, each of which is allocated to a user; and CDMA allocates to each user a pseudo random code with good auto-correlation and cross-correlation property, thus multiple users can simultaneously send signals within the same bandwidth. TDMA and CDMA generally use FDMA to divide their frequency band into smaller ones, and then perform time division or code division. SDMA utilizes space irrelevance to obtain multiple access capability.
As for these traditional multiple access technologies, since the base station and the terminal send signals with a single carrier frequency or on a narrow band, it is more suitable for supporting low-speed voice services. For high-speed data services, there is relatively severe inter-symbol interference in a single carrier frequency system or narrowband system, thus the requirement for the equalizer of receiver is higher. For those multiple access technologies which support conventional multi-carrier, it is required to use filter banks to separate signals at the receiver side. This kind of multiple access technologies are simple to implement, however, they have the disadvantage of low spectrum efficiency.
OFDMA, which supports high-speed data service, divides the channel band into different sub-channels, and several users can simultaneously send signals on different bands. An OFDMA system can effectively reduce inter-signal interference through serial-parallel conversion of the high-speed data, thus reduce the complexity of the receiver. Moreover, the OFDMA system utilizes orthogonality between the sub-carries to allow the spectrum of the sub-channels to overlap with each other, so that the usage of spectrum resource can be maximized. Compared with a single carrier system, however, the OFDMA system has relatively higher peak-to-average power ratio.
With the development of wireless communication technology, especially the development of multiple access technologies, categories of the wireless terminals as well as types of the services that can be supported are also greatly enriched. Besides all kinds of handheld terminals, the fixed terminals and the application of notebook computer are also an important part. Basically, because of their size and cost, the handheld terminals require smaller power consumption, thus traditional single-carrier multiple access technologies such as SC-FDMA (single carrier frequency division multiple access) can be applied to support low-speed voice service. The fixed terminals and notebook computers can use power supply or other stable power equipment, thus can provide the users with high-speed data services and as a result, the multiple access technology of OFDMA can be applied.
In the present wireless communication system, the base station only supports terminals with a single multiple access technology. For example, in a CDMA communication system, the base station only supports the terminals whose uplink and downlink both apply CDMA. In an IEEE (Institute of Electrical and Electronics Engineers) 802.16e system, the base station only supports the terminals whose uplink and downlink both apply OFDMA.
However, with the development of wireless communication technology, for different multiple access technologies, there is an increasing need for a communication system capable of supporting different multiple access technologies with the same carrier frequency.